The greatest utility of the invention described in this specification is for inspection of piping, but the invention can be used to inspect other types of hollow containers such as heat exchangers and silo sections used to transport fluids. Piping is vulnerable to attack by internal and external corrosion, cracking, mechanical damage and manufacturing flaws in the manufacturing process as well as needs to remain undamaged during use in the field. Therefore the invention has applicability both before and after installation. Anomalies and flaws can be caused during manufacturing and need to be discovered prior to installation. In addition, physical, chemical and electrolytic actions can cause flaws such as cracks after installation and therefore regular inspection is required to ensure safe operation. Furthermore, in order to minimize energy losses and increase worker safety piping is usually insulated by an external layer of thermal insulation around the outside diameter of the piping. This layer of insulation makes it more difficult to inspect the piping for flaws. Inspection of piping after installation is more problematic because of the difficulties of access and in the case of piping inspection the apparatus needs to be capable of use over long distances in remote locations. Piping has to be inspected completely around the circumference to detect possible flaws in every portion of the pipe. This requirement further complicates the piping inspection process.
Various methods have been described in the prior art to detect flaws in piping. For example ultrasonic inspection systems have been used. Ultrasonic inspection requires that a sound wave be induced into the surface of the pipe. Typically an electronic generator or transducer generates pulses or periodic sound waves. These sound waves can either be directed along the length of the pipe or perpendicular to the pipe wall. These methods are referred to as shear wave and straight beam respectively. The sound waves bounce of the pipe walls and also off anomalies or discontinuities and the echoes are measured by a receiving transducer. The speed of the echoes are measured to develop an accurate description of the internal nature of the pipe walls. Most piping is insulated to minimize energy losses and increase worker safety. Typically the piping is wrapped with layers of insulating foam and surrounded with a protective layer of stainless steel or aluminum. The primary drawback of the ultrasonic systems is that intimate contact of the generator with the pipe surface is required. Because sound waves are reflected by the insulation layer the insulation and protective layers need to be removed from the pipe for accurate inspection by ultrasonic devices.
Radiographic techniques have been used to inspect piping and hollow vessels. X-rays for example being electromagnetic waves are unaffected by the insulation layer. X-rays penetrate the insulation as well as the pipe wall and impinge on X-ray receptive film that captures the images of the vessel or piping. After the film is exposed to the radiation it needs to be developed. One needs chemicals to develop the image on the film and these chemicals need to be safely disposed. The entire process can take ten to fifteen minutes per film image. When imaging a pipe of six or more inches in diameter, three or more images are necessary to ensure complete coverage of the pipe. Pipes greater than 12 inches in diameter require additional images needing more time and more chemicals to dispose.
Internal pipe crawling devices equipped with X-ray equipment have been described in the prior art. The external X-ray source and the internal X-ray detector need to be aligned for the X-ray detector to receive the data signals. One has to ensure that during the movement of the device that it does not climb the internal walls thereby causing rocking motions and disturbing the alignment of the X-ray source and the detector. If the X-ray source and the detector are not aligned then the accuracy and quality of the resulting images are adversely affected. It may also be necessary to stop fluid flow in the piping during the inspection process.